A vast body of research examined changing employment relations and the ensued employment precarity. However there is a lack of quantitative tools able to assess the extent and impact of precarity overtime and at the individual level. Using the index of complexity as a starting point, we aim to create an index of precarity accounting for the benefit or loss entailed by each transition. Including the nature of each transition and the unpredictability of the whole employment trajectory in the index allows researchers to grasp both the complexity and the quality of young people's employment trajectories. Our contribution shows how the proposed index provides a synthetic measure for comparing the degree of precarity. Results from a school-to-work transition dataset confirm the usefulness of the index as a predictor of future negative labour market trajectories.